Two-way fast acting bimetal control elements



, Feb. 4, .1958 D. H. MCCORKLE, SR 2,821,836

TWO-WAY FAST ACTING BIMETAL CONTROL ELEMENTS Filed Nov. 20, 1953 FIG.

BYW

United States Patent TWO-WAY FAST ACTING BIMETAL CONTROL ELEME D. H. McCorkle Company, Berkeley, Calif., n corporation of California Application November 20, 1953, 'Serial No. 393,254 Claims. (CI; 60-43) This invention relates to heat motors, and more particularly to a modified and improved form of-the twoway fast acting bimetal type of heat motor described and claimed in my co-pending application, Serial Number 348,275, filed April 13, 1953, now Patent No. 2,743,574, issued May 1, 1956.

In my mentioned co-pending application, I therein summarized my invention as being a bimetal heat motor comprising a pair of attached bimetalstrips so disposed as to be oppositely acting with respect to each other under the influence of temperature change, with means associated therewith to proportion the heating and the rate of cooling of both strips.

The present invention has for its primary object the provision of improved means to proportion the rate of heating and the rate of cooling of both strips, whereby a more efiicient and faster acting heat motor may be obtained, along with economies in the cost of manufacturing and assembling the heat motor.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the drawing forming part of this specification, and in which:

Figure 1 is a top plan view of the improved heat motor of the invention;

Figure 2 is a view in section taken along lines 22 of Figure 1;

Figure 3 is an enlarged view in section taken along lines 33 of Figure 1;

Figure 4 is a semi-schematic view in side elevation of the improved heat motor of the invention in a neutral position, and

Figures 5, 6 and 7 are semi-schematic views in side elevation of the subject heat motor, illustrating sequential operating positions of the same.

Referring to the drawing, the heat motor comprises a first bimetal strip 10 and a second bimetal strip 12 secured in end to end relation with strip 10, as by butt welding. The bimetallic characteristics of strips 10 and 12 are similar, but strip 12 is inverted with respect to strip 10.

Means are provided to both heat and cool strip 10 at a faster rate than strip 12, said means comprising an electrical circuit 14 which includes therein: a transformer 16; a thermostat control 18; and a continuous resistance winding 20 wrapped around and carried by an edge-notched mica strip 22, the latter being sandwiched between separate mica strips 24 and 26. Carrier strip 22 and covering strips 24 and 26 are, as a group, anchored at one end between mica strip 28 and a laminated mica takeofi head 30, as by hollow, or sleeve type, rivets 32. The ends of resistance winding 20 extending outwardly from between mica elements 28 and 30 and extend downwardly through hollow rivets 34, which serve to keep the layers or laminations of mica block 30 together, to points of connection with circuit 14. In this manner, the resistance winding 20 is fully insulated from bimetal strip 10, and this insulation is achieved without the use of any sheathtype covering for strip 10, such as was employed in the heat motor of my mentioned co-pending application. Such a sheath-type insulation evidently has an inhibiting effect on the flexing of the bimetal strip.

The free ends of the mica strips 24 and 26, which strips are longer than intermediate strip 22, are maintained in juxtaposed relation to the inner end of strip 12 by means enabling relative sliding movement between the mica strips and strip 12, said means comprising a tongue 36 defined in strip 12 by slots 38. The free end of tongue 36 engages the underside of mica strip 26. Other slots 40 may be provided in bimetal strip 12, and these, together with slots 38 and centrally disposed open-ended slot 42 formed in bimetal strip 10, serve to minimize transverse warping or curling of the strips under the action of heat.

The heat motor above described may be employed in any environment, such as with the diaphragm type gas control valve shown in my mentioned co-pending application, wherein it is desired that a given element be com trolled by the two-way fast-acting movement of the free end of bimetal strip 12 under the action of temperature change.

When circuit 14 is energized under the control of, for example, thermostat element 18, heating of resistance winding 20 causes bimetal strip 10 to rapidly rise in temperature, and causes strip 12 to more slowly rise in temperature due to the heat conduction connection between strips 10 and 12. Shortly after circuit 14 is thus energized, strips 10 and 12 are moved out of the neutral position of Figure 4 to the position of Figure 5, wherein strip 10 has been warped upwardly, but strip 12, which is inverted with respect to strip 10 and therefore warps downwardly under an increase in temperature, remains relatively straight. Such initial movement of the free end of the compound strip constitutes a quick acting one way movement which may be employed for the purposes mentioned in my said co-pending application.

As the circuit 14 remains energized and the heat input to strip 10 directly, and to strip 12 indirectly, or by conduction, continues, strip 12 gradually becomes downwardly warped. However, when strip 12 reaches its maximum temperature condition the free end of strip 12 is still disposed above the neutral position, i. e., the overall position of the compound strip is an upwardly warped position, as shown in Figure 6. Strip 12, of course, never reaches the temperature level of strip 10.

When circuit 14 is de-energized, strips 16 and 12 begin to cool. However, strip 10, which, due to the positioning of resistance winding 20 adjacent thereto, has been heated to the highest temperature, cools at a greater rate than strip 12, the result being that there is an overall rapid movement of the compound strip downwardly from the position of Figure 6 to the position of Figure 7, such movement being efiective to quickly bring about a rapid re-positioning of the element controlled by the compound strip, such, for example, as the type of element disclosed in my said co-pending application. As strip 12 continues to cool it eventually reaches the neutral, or horizontal, position shown in Figure 4, but the connection between the free end of the compound strip and the element to be controlled thereby may be made such as to render this delayed upward warping, due to final cooling, of strip 12 ineffective to reverse the operating position of the element controlled by the compound strip. In other words, the degree of movement of the compound strip in going from the Figure 4 to Figure 5 positions is such as to cause a change in the operating position of the element, while the degree of movement of the strip in going from the position of Figure 7 to that of Figure 4 is insufiicicnt to cause a change in the operating position of said element.

t is to be pointed out that as strip 12 is caused to warp reversely with respect to strip 10, the warping of strip 12 tends to maintain the end of tongue 36 in closely positioned relation, or engagement, with the free ends of mica strips 24 and 26. There is, however, no such clamping action between the tongue and these strips as to constitute sufiicient frictional resistance to tend to inhibit the freedom of fiexure of either of strips 10 or 12.

In practice, the improved heat motor of the subject invention has been found to be very fast-acting in both directions of its element control movement. When coupled to a valve of the type described in my mentioned copending application, the heat motor has acted to open the valve within nine seconds from the time of energization of circuit 14 and to close the valve within seventeen seconds from the time of de-energization of circuit 14.

While a specific embodiment of the improvement heat motor of the invention has been shown and described, it is to be understood that all substantial equivalents thereof are within the spirit and scope of the invention.

What is claimed is:

l. A heat motor comprising a first bimetal strip having a mounting end, a second bimetal strip inverted with respect to said first strip and secured to the other end of said first strip in heat transfer relation therewith, said second strip having heat response characteristics substantially similar to those of said first strip, resistance heating means and carrier means therefor disposed at one side of said first strip in juxtaposed relation thereto, insulating means for electrically insulating said heating means from said first strip, the other side of said first strip and both sides of said second strip being exposed to the atmosphere, means for securing the end portions of said insulating means and carrier means to the mounting end of said first strip, and means for maintaining the balance of said insulating means and carrier means in juxtaposed relation with said first strip while allowing for free relative movement between said first strip and said insulating and carrier means during heat responsive movement of said strips.

2. A heat motor as set forth in claim 1 wherein said heating means comprises a wire wound around a thin mica strip constituting said carrier means, and wherein said means for insulating said wire comprises a pair of mica strips, one in overlying and one in underlying relation to said first-mentioned mica strip.

3. A heat motor as set forth in claim 2, said means for maintaining said insulating and carrier means in juxtaposed relation to said first strip comprising a tongue defined in said second strip, said tongue extending in the direction of said first strip and having the end thereof disposed in overlapping and non-binding relation with the ends of said pair of mica strips.

4. A heat motor comprising a first bimetal strip having a mounting end, a second bimetal strip inverted with respect to said first strip and secured to the other end of said first strip in heat transfer relation therewith, said second strip having heat response characteristics substantially similar to those of said first strip, resistance heat- .ing means disposed at one side of said first strip, carrier means for said heating means, means for electrically insulating said heating means from said first strip, said carrier means and insulating means being connected at one end thereof to the mounting end of said first strip, and means forming a portion of one of said strips adapted to maintain the other end of said carrier and insulating means in substantially juxtaposed relation to said first strip without inhibiting temperature-responsive fiexure of either of said strips.

5. A heat motor according to claim 4, said first bimetal strip having the other side thereof exposed to the atmosphere and said second strip having both sides thereof exposed to the atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 1,212,260 Reeve Ian. 16, 1917 1,292,773 Hertzberg Jan. 28, 1919 1,336,728 Christensen Apr. 13, 1920 1,656,706 Hann Jan. 17, 1928 1,858,082 Foucault May 10, 1932 2,227,901 Hageman Jan. 7, 1941 2,336,408 Matthews Dec. 7, 1943 2,441,805 Fell May 18, 1948 2,673,444 Clapp Mar. 30, 1954 

